The present invention relates to coated recoverable articles for use in protecting elongate substrates, and more particularly to coated recoverable articles for the environmental sealing of joints in insulated district heating or cooling pipes.
Recoverable wraparound or tubular sleeves are used to provide environmental protection for elongate substrates such as pipelines, by acting as a barrier to moisture or solvent penetration or to mechanical damage. Such sleeves may comprise a cross-linked polyolefin material coated with a mastic or other sealant. The sleeves are preferably heat recoverable, which means that their dimensional configuration can be made to change substantially when subjected to heat. They will usually recover, on heating, towards an original shape from which they have previously been deformed, but the term "heat recoverable" as used herein also includes an article which on heating adopts a new configuration even if it has not been previously deformed.
When district heating pipes, which typically consist of a steel transport pipe insulated by a foam and an outer polyethylene jacket, are to be joined, a length of insulation is first removed from the transport pipe to allow access thereto. Joints between transport pipes are generally made by welding and the heat required would damage any insulation close to the weld line. After the transport pipes have been welded the insulation must be made good across the weld, and one way of doing this is to encase the exposed regions of transport pipe using thin half-shells of sheet material which define a space around the pipe for subsequently filling with an insulating material. Since the material of many types of insulation and also the transport pipes themselves may be impaired by the presence of water, it is usually necessary to provide a water seal when making good this insulation. Such a seal may be provided across the entire joint or, at least around each end of the pair of half-shells and the adjacent pipe insulation. This seal can be provided by a mastic coated recoverable sleeve, for example as described in No. GB-1483113, or more preferably by a sleeve having a band of a heat-activatable adhesive towards each circumferentially extending edge and a band of a mastic between them, as disclosed in No. GB-A-2108625, the disclosure of which is incorporated herein by reference.
The installation of the mastic/adhesive coated sleeves is discussed in the latter published patent application. Briefly, the substrate to be protected is gently pre-heated and the recoverable sleeve is placed in position. This pre-heating reduces installation time and improves bonding. If the sleeve is a wraparound sleeve, it is secured in the wrapped configuration by an adhesive coated path or a mechanical closure. Subsequent application of heat to the sleeve causes:
(a) shrinkage of the sleeve into contact with the pipe or the insulation;
(b) flow of the mastic under the compressive force of the sleeve, so as to fill any voids which may otherwise exist between irregularities on the surface of the pipe or insulation and the recoverable sleeve; and
(c) activation of the adhesive so as to form an annular bond between the sleeve and the underlying pipe or insulation.
The installed sleeve provides good environmental sealing, the mastic accomodates thermal expansion and contraction of the substrate, and the adhesive provides the sleeve with improved resistance to soil stress movement.
The joint region is preferably insulated by foamed material, for example by means of pre-formed foam pieces or a liquid foamable material, for example, a foamable polyurethane. As disclosed in No. GB-A-2108625, liquid foamable material may be supplied into a cavity formed between the transport pipes and a hollow casing which surrounds the transport pipes and overlaps the existing pipe insulation at each end. The foamable material may be supplied to the cavity before or after the casing is sealed to the pipe insulation by means of a sleeve, but it is preferred to provide the insulation after making the seal so as to reduce installation time and also to reduce leakage of foam from the cavity. Thus, waste can be minimised and the quality of the insulation can be better controlled. However, while sealing of the cavity before foaming is desirable, the technique suffers from the disadvantage that hitherto, special methods have been required if ballooning of the recoverable sleeve, under the foaming pressure, is to be avoided. A further disadvantage of the existing sleeve is that pressure testing of the seal provided by the sleeve, before foaming, may also lead to ballooning and the formation of leaks.